1. Field
The disclosed concept pertains generally to electrical enclosures and, more particularly, to such electrical enclosures structured to resist internal arcing faults. The disclosed concept also pertains to methods of resisting pressure caused by arcing faults.
2. Background Information
Electrical equipment such as, for example and without limitation, electrical busways, relays, circuit interrupters, electric meters and transformers, are typically housed within an electrical enclosure such as, for example, a housing, such as a box, cabinet, module or compartment, to protect the electrical equipment.
Electrical enclosures can enclose a wide range of electrical equipment, such as, for example and without limitation, medium voltage motor starter(s), low voltage switchgear, low voltage motor control center(s), low voltage switchboard(s), low voltage panelboard(s), and medium and/or low voltage transfer switches.
Switchgear typically includes a combination of an electrical busway and electrical disconnects, fuses and/or circuit breakers employed to electrically connect and disconnect electrical equipment. As one non-limiting example, switchgear includes an assembly of one or more motor starters that can also contain circuit breakers and fused switches. Example switchgear devices include, but are not limited by, a circuit interrupter, such as a circuit breaker (e.g., without limitation, low voltage; medium voltage; high voltage); a motor controller/starter; and/or any suitable device which carries or transfers current from one place to another.
Arc resistant switchgear is intended to mitigate the effects of internal arcing or arc flash outside of the electrical enclosure (e.g., without limitation, low voltage; medium voltage; high voltage). Unintended internal arcing faults can occur from a variety of causes (e.g., without limitation, accidental dropping of tools; the presence of animals; insulation failure).
Excessive pressure resulting from an unintended internal arcing fault can cause damage to the electrical enclosure resulting in hot gases, molten copper and steel escaping the electrical enclosure and creating a potential hazard. Hence, it is highly desirable to reduce internal pressures generated during an arcing fault, in order to reduce the chance of hot gases escaping from the electrical enclosure.
FIG. 1 shows a three-phase electrical busway 2 including back-connected (e.g., electrically connected to a surface facing the rear of the corresponding electrical enclosure (not shown)) power cables 4. The fault current path 6 in, for example, the bus members 12,10 provides a generally downward (with respect to FIG. 1) JxB force 14 that elongates the phase-to-phase arc 16. Similarly, another JxB force 15 elongates the other phase-to-phase arc 18 between bus members 10,8. Convective forces 20 attempt to lift (with respect to FIG. 1) the arcs 16,18 resulting in an angled downward (with respect to FIG. 1) direction 22 thereof as shown. The elongated arcs 16,18 increase the corresponding arc voltage and arc power and, thus, increase the pressure created in the corresponding electrical enclosure (not shown). Although not shown in FIG. 1, arcs (not shown) on the outer phases 24,26 attach to adjacent electrical enclosure walls (not shown).
Frequently, auxiliary equipment (e.g., without limitation, a voltage transformer; a control power transformer; a fuse truck; other electrical equipment) is employed in a location within an electrical enclosure where an unintentional arc may result that is relatively close to an outside door. This is less desirable from a safety standpoint as an arc in another controlled location of such electrical enclosure.
There is room for improvement in electrical enclosures including an electrical busway.
There is also room for improvement in methods of moving arcing faults in electrical enclosures.